1. Field of the Invention
The present invention relates to a data communications apparatus and, more particularly, a data communications apparatus capable of performing bidirectional data communications through a cable network. This application for a communications apparatus is based on Korean patent application No. 2004-70119, which is incorporated by reference herein for all purposes.
2. Description of the Related Arts
The most common methods for implementing high-speed Internet subscriber network include the use of a DSL modem or a cable modem, which transmits and receives digital data through an existing twisted wire pair or a cable TV network, respectively. While the DSL modem is cost-effective in case that cable TV lines are broadly installed to a large majority of residences, the cable modem may be more effective alternative if cable TV lines are available in most of the residences. In a data communications network based on the cable TV network, each subscriber premise is connected to or equipped with a cable modem, which communicates with a counterpart, i.e., a headend to help the subscriber premise with Internet access.
FIG. 1 illustrates an example of a data communications system based on the cable TV network. In the system shown in FIG. 1, a headend or a cable modem termination system (CMTS) 10 is connected to a plurality of cable modems 34A, 34B through a tap 20 and/or a splitter 30. The CMTS 10 is connected to an Internet service provider (ISP) server 12, and the cable modems 34A, 34B are connected to client PCS 36A, 36B, respectively. The CMTS 10 modulates data to be transmitted from the ISP server 12 to a client PC 34A or 34B to transmit through the cable network, so that a desired cable modem 34A, for example, demodulates such data to provide to the client PC 34A. Similarly, the cable modem 34A modulates data generated by the client PC 34A to transmit to the CMTS 10, so that the CMTS 10 demodulates such data to provide to the ISP server 12.
Generally, a cable network equipment is manufactured to be compliant with Data Over Cable Service Interface Specification (DOCSIS) proposed by Multimedia Cable Network System (MCNS) and IEEE802.14 standard proposed by Institute of Electronic and Electrical Engineering (IEEE). According to the DOCSIS standard, the CMTS modulates the downstream data by 64 Quadrature Amplitude Modulation (QAM) or 256 QAM scheme in a frequency band of 5 MHZ to 45 MHZ to provide a data rate of 20 Mbps to 30 Mbps. The cable modem modulates the upstream data by Quadrature Phase Shift Keying (QPSK) or 16 QAM scheme in a frequency band of 65 MHZ to 750 MHZ to provide a data rate of 200 Kbps to 10 Mbps. Meanwhile, regarding medium access control (MAC), frequency domain multiple access (FDMA)/time division multiplexing (TDM) is used to facilitate communication from the CMTS to each cable modem and FDMA/time domain multiple access (TDMA) is used to facilitate communication from each cable modem to the CMTS.
However, the conventional CMTS and cable modem adopting FDMA or TDMA along with TDM are disadvantageous in that it is difficult for them to provide high data rates, for example, above 50 Mbps. Besides, the conventional CMTS and cable modem has drawbacks that they are much complex in their hardware configuration and show less reliability because different frequency bands and modulation schemes are used for the transmission of upstream and downstream data.